The Davenport multi-spindle automatic screw machine, originally built in the early 1900's, is a screw machine that has had few major design changes made to it since its' early construction. As a result, parts made for new machines today are able to fit older machines, and it is one of the least expensive screw machines to maintain.
Heretofore, several patents and publications have disclosed aspects of and improvements to Davenport screw machines:
U.S. Pat. No. 5,910,201 to Muscarella et al., issued Jun. 8, 1999 for a “MULTIPLE SPINDLE SCREW MACHINE,” incorporated herein by reference in its entirety,
U.S. Pat. No. 6,219,895 to Muscarella et al., issued Apr. 24, 2001 for a “MACHINE TOOL WITH SERVO DRIVE MECHANISM” and its related continuing application patents (U.S. Pat. No. 6,263,553 and U.S. Pat. No. 6,421,895), each of the above patents being individually incorporated herein in their entirety by reference; and
“The Davenport 5 Spindle Automatic Screw Machine Model B, Instruction Book,” Davenport Machine, P.O. Box 228, Rochester, N.Y. 14601 (1983 Edition); Revised Version Printed May 30, 1987, which is also incorporated herein by reference in its entirety.
In general, the Davenport screw machine, such as the Model B (Prior Art FIG. 1), is designed to manufacture parts at rates from 120-4500 pieces per hour. Most parts are made complete with no secondary operations, thereby reducing the overall cost of the part. The Davenport screw machine 110 is designed for high volume low cost production, and is particularly well suited to produce threaded parts, both internal and external, as well as slots, flats, holes, recesses, trepans and knurling for example. The Davenport screw machine operates on bar stock inserted into collets associated with one of a plurality (five) of workstations on one end of the machine. Then the workstations index around to various tools that cut the stock down to the finished part—performing a different machining operation at each tool. Once complete, the part is separated from the stock and ejected away from the tooling area, where it is collected with other parts. Although the tooling and set up for a particular part may be somewhat time consuming, the machine will then be capable of reproducing many such parts.
Referring to FIG. 1, there is shown a screw machine 100 having a motor 102 is connected via pulleys 104 to a gear assembly 106, which in turn drives a bevel gear set 108. The gear assembly 106, including bevel gear set 108 directs operating power from the motor 102 to a drive shaft 110 and to another coupled drive shaft 112 extending perpendicularly to the drive shaft 110. The drive shaft 110 extends to a rear worm 116, which drives a gear 172. The gear 172 causes rotation of an end cam shaft 174, which in turn rotates a plurality of tool spindle cams 176. The tool spindle cams 176, in turn, effect the operation of end tools (175) that are mounted on the stationary head 177. The drive shaft 168 drives a front worm 180, which drives a gear 182. The gear 182 in turn drives a side cam shaft 184 to cause rotation of a plurality of cross slide and tool cams 186 and a locating cam 188. The drive shaft 184 also causes rotation of a chuck and feed cam 190. The drive shaft 168 and gear assembly 106 are used, in general to control the rotation and indexing of the revolving head 120, collets 122, Geneva disc 124, and the various tool arms 126 in accordance with the well-known operation of the Model B machine. Also driven from motor 102 is a lubricator 190 and, indirectly, an oil pump 192.
As described in prior patents (e.g., U.S. Pat. No. 6,219,895) one problem with conventional screw machines is a lack of control over the indexing drive mechanism, which may be independent from the spindle drive mechanism. The cam shaft and indexing drive mechanism, as illustrated in FIG. 2, is driven by a single servomotor, and a variable frequency drive motor operates the spindles of the machine tool. Furthermore, a computer control system controls and monitors the operation of the machine tool. As depicted in prior art FIG. 2, the servomotor 146 is operatively connected to a gear box 156, which in turn drives a bevel gear set 158 through a coupling 160. The bevel gear set 158 directs operating power from the servomotor 146 to a drive shaft 166 and to another coupled drive shaft 168 extending perpendicularly to the drive shaft 166. The drive shaft 166 extends to a rear worm 170, which drives a gear 172. The gear 172 causes rotation of an end cam shaft 174, which in turn rotates a plurality of tool spindle cams 176. The drive shaft 168 drives a front worm 180, which drives a gear 182. The gear 182 in turn drives a side cam shaft 184 to cause rotation of a plurality of cross slide cams 186 and a locating cam 188. The drive shaft 184 also causes rotation of a chuck and feed cam 190 and an absolute encoder 192.
The disclosed embodiments are directed to an electromechanical spindle and camshaft drive system to replace and improve existing mechanical systems common to multi-spindle machine tools such as the Davenport Model B as generally depicted in FIG. 1. Generally, a common power source is used in the Model B to drive main spindles and/or camshafts though a series of shafts, gears, clutches, and gear reductions. One embodiment disclosed herein uses a programmable logic or similar controller to control operation the main spindles, both camshafts and threading axes, all independently of one another. The independent axes are driven by associated servomotors and controlled by a code-driven logic controller though ladder logic. The disclosed system will transform, and be suitable for use on, existing multi-spindle machine tools such as a Davenport Model B; making them more productive, more efficient and significantly reducing setup/run-in and maintenance requirements that are a burden in existing systems. The disclosed embodiments allow the elimination of integral systems inherent in “old” screw machine technology incorporating bushings, and worm or similar drives that are subject to mechanical wear of one type or another. The replacement system disclosed herein is more efficient, with lower associated replacement costs.
Productivity and efficiency of existing multi-spindle machine tools will improve because fewer mechanical parts (e.g., shafts, bushings, gears, clutches, and gear reductions) are used and the system is more reliable and repeatable than traditional mechanical systems because of the electronic controls and replacement of several busing assemblies with precision bearings. Furthermore, maintenance requirements are reduced due to the reduction in the number of service parts required. In addition, accessibility to various subassemblies and adjustment positions on the existing multi-spindle machine tools is greatly improved through modified mechanical design and independent drive motors, further reducing labor costs for maintenance.
In accordance with the one embodiment, there is provided a multiple spindle screw machine, comprising: a frame; a spindle supporting head operatively associated with the frame for indexible rotation; a plurality of work-supporting spindles mounted in said spindle supporting head for rotation therewithin and relative thereto about parallel axes radially spaced from and angularly spaced about a spindle drive shaft; a spindle drive, operatively connected to the spindle drive shaft, to effect rotation of the work supporting spindles, and lengths of stock carried thereby, about axes of rotation defined by the work supporting spindles; a side servomotor operatively connected to a side cam shaft to effect rotation of a plurality of side cams independently of the operation of the spindle drive, said side cam shaft extending parallel to the axes of rotation defined by the working spindles; side cams mounted on said side cam shaft, for rotation thereby and to cause operation of side machining tools thereby machining the lengths of stock; an end servomotor operatively connected to an end cam shaft and extending perpendicularly to the axes of rotation defined by the working spindles; at least one end cam mounted on the end cam shaft for rotation thereof independently of the operation of the spindle drive, and to cause operation of an end machining apparatus, thereby machining the lengths of stock carried by the work supporting spindles; and a multi-axis controller for controlling the operation of the spindle drive, the side servomotor and the end servomotor.
In accordance with another embodiment, there is provided a multiple spindle screw machine, comprising: a frame; a spindle drive shaft mounted on the frame for rotation about a stationary axis; a spindle supporting head mounted on the frame for indexible rotation coaxially about said spindle drive shaft; a plurality of work-supporting spindles mounted in said spindle supporting head for rotation therewithin and relative thereto by said spindle drive shaft about parallel axes spaced radially and angularly about said spindle drive shaft; a servomotor spindle drive operatively connected to the spindle drive shaft to effect rotation of the work supporting spindles and lengths of stock carried thereby; a side cam shaft extending parallel to the axes of rotation defined by the working spindles; a plurality of side machining tools positioned adjacent one another and along a line substantially parallel to the side cam shaft; a plurality of side cams, mounted on the side cam shaft, for rotation thereby to cause operation of said side machining tools thereby machining the lengths of stock; an indexing mechanism driven by the side cam shaft for sequentially indexing each of the working spindles through a plurality of workstations; an end cam shaft extending perpendicularly to the axes of rotation defined by the working spindles; at least one end machining apparatus positioned adjacent the end cam shaft; at least one end cam mounted on the end cam shaft for rotation thereby to cause operation of the end machining apparatus thereby machining the lengths of stock carried by the work supporting spindles; a side servomotor; means operatively connecting the side servomotor to the side cam shaft to effect rotation of the side cams independently of the operation of the spindle drive; an end servomotor; means operatively connecting the end servomotor to the end cam shaft to effect rotation of the end cams independently of the operation of the spindle drive; and a multi-axis controller for controlling the operation of the speed spindle drive means and the two servomotors.
In accordance with a further aspect of the disclosed embodiment, there is provided a method of operating a multiple spindle screw machine using a multi-axis controller, comprising: operating a spindle drive, operatively connected to a spindle drive shaft, to effect rotation of a plurality of work supporting spindles, and lengths of stock carried thereby, about axes of rotation defined by the work supporting spindles; in response to the controller, operating a side servomotor, operatively connected to a side cam shaft, to effect rotation of a plurality of side cams independently of the operation of the spindle drive, said side cams causing the operation of side machining tools to thereby machine the lengths of stock; operatively connected to an end cam shaft and extending perpendicularly to the axes of rotation defined by the working spindles, to cause the operation of an end machining apparatus independently of the operation of the spindle drive, and, thereby machining the lengths of stock carried by the work supporting spindles; and controlling the operation of the spindle drive, the side servomotor and the end servomotor.
One aspect of the disclosure deals with a basic problem in the afore-described prior art machines—that of the need for a large, expensive servomotor to drive the connected cam shafts (drive shafts 166 and 168 in FIG. 2) used to operate the tooling. Moreover, the prior art devices continue to utilize various mechanical parts (e.g., shafts, gears, clutches, and gear reductions) so as to operate the screw machine with a servomotor. Such parts are subject to various dimensional tolerances and wear, leading to the need to stock replacement mechanical parts. This aspect is further based on the discovery of a technique that alleviates this problem. The technique utilizes at least two independent, yet electronically synchronized, servomotors to replace the single servomotor of the prior art and various mechanical parts, particularly those that are known to be subject to wear. Such a substitution is not only less expensive, but enables the elimination or reduction of the wearable parts and will thereby assure accurate and reliable operation of the screw machine for longer periods of time, and consistent quality of parts produced thereon. Furthermore, by eliminating the unnecessary components, the disclosed embodiment “opens up” the screw machine so that necessary adjustments and maintenance may be more easily performed than is the case in the conventional and prior art systems. For example, set up of the machine is improved as the cross-slides no longer interfere.
The system and techniques described herein are advantageous because they are less expensive compared to other approaches, and make it unnecessary to utilize a single, large servomotor to operate components of the screw machine. The techniques are advantageous because they further acquire and operate on feedback from the independent servomotors employed to facilitate the control of the machine as well as the identification and isolation of any operational problems at an early stage. As a result of the improved design, it is possible to build or retrofit an automatic screw machine wherein a multi-axis controller controls at least the speed of the spindle drive in conjunction with the two servomotors operating the tooling cams, and where the independent operation of at least the two servomotors may be electronically synchronized. It will be appreciated that one disclosed embodiment, employs the aforementioned multi-axis controller to control the spindle drive and a threading drive or other tooling operation so as to further improve the synchronized operation of the screw machine and reduce the number of mechanical components (e.g., gears) required for operation of the machine.
The following disclosure will be presented in connection with a preferred embodiment, however, it will be understood that there is no intent to limit the embodiment described. On the contrary, the intent is to cover all alternatives, modifications, and equivalents as may be included within the spirit and broad scope defined by the appended claims.